Gas masks are used as personal protection gear to protect the user from inhalable toxic substances and toxic environmental substances. The field of use lies in occupational safety and especially in firefighting. Half masks or full masks are used for this, which supply the user with filtered ambient air or clean air from compressed air cylinders.
The masks protect the user especially well against environmental effects by sealing the face, especially the mouth and nose, against the environment with the mask body. This means, however, on the other hand, that speech is transmitted from the sealed mask to the outside space only poorly, because the materials greatly muffle speech. Verbal communication between gas mask users is therefore problematic.
Speech diaphragms, which are said to improve transmission of the user's speech through the mask to the outside, are frequently integrated in prior-art gas masks. The speech diaphragm consists of a thin plastic film or metal foil, which is fastened gas-tightly in an opening of the mask body. The speech diaphragm is stimulated by the sound in the interior of the mask and vibrates correspondingly, as a result of which it transmits corresponding sound waves itself to the outside. While the prior-art solutions are well suited for low-frequency sound components, the transmission of frequencies above 1 kHz is limited. The transmission function of the speech diaphragm is consequently frequency-dependent and decreases with rising frequency. This leads to distortions and compromises the intelligibility of speech, because the components with high frequencies are especially important for the intelligibility of speech.
An oxygen inhalation mask is known from DE 699 19 907 T2. A horn or a funnel is arranged in front of the user's mouth in the interior space of this mask. A microphone capsule is arranged in the smaller opening of the funnel pointing towards the user's mouth. The funnel is said to bring about focusing of the sound waves towards the microphone capsule.